1. Field of the Invention
The present invention relates to a weighing apparatus for use in determining whether to activate an air bag system intended for a passenger seat in order to protect a person in a vehicle, for example, from a collision accident, and to more particularly to a weighing apparatus for weighing a person on board from internal pressure in air bags adapted to receive the weight of the person. Also, the present invention relates to an apparatus for detecting an auxiliary-seat mounting direction in order to determine whether an auxiliary-seat such as a child seat for protecting a child from a vehicle accident in forward- or backward-turned when the auxiliary seat is mounted on a passenger seat. Further, the present invention relates to a person-on-board protecting apparatus capable of controlling the expansion force (or expansion rate) of an air bag or the like in accordance with the seating condition of a person on board. Still further, the present invention relates to an apparatus for giving a warning about a seating condition when the seating condition of a person on board is bad in order to inflate an air bag effectively. Yet still further, the present invention relates to an apparatus for detecting the presence of a person on board, for example, a child standing without sitting on a seat during traveling or a so-called standing child.
2. Description of the Related Art
A weighing apparatus similar in type to the captioned apparatus has been designed to weigh a person sitting on a seat from the output voltage of a plurality of piezoelectric elements provided in the form of a sheet for the seat, for example, a passenger seat.
However, such a weighing apparatus is installed on the seat and the person on board is to sit directly on the seat. Consequently, it is difficult to protect the elements from external force and the problem is that the elements are easily damaged. When the sheet and connectors are electrically connected, moreover, the connectors are exposed outside and have to be protected without spoiling the external appearance and causing connection failure.
A person-on-board restraining system of a type similar to the captioned apparatus for detecting the weight of a person on board who is sitting on a seat has been described in, for example, Japanese Patent Laid-Open No. 186880/1995 Publication. Such a system will be described first by reference to FIGS. 15-16.
When a person on board sits on the seat portion 202 of a seat 201, a weighing sensor 203 using a plurality of strain meters 203a embedded within the seat 201 weighs the person, and a signal indicating the detected weight is supplied to a control unit 204. The control unit 204 is also supplied with a signal resulting from the detection of the reclining angle of the back portion 205 of the seat 201 by means of an angle sensor 206. The signal supplied from the weighing sensor 203 is corrected by the signal detected by the angle sensor 206 in the control unit 204, so that the actual weight of the person on board who is sitting on the seat. When it is judged that no person on board is sitting on the seat, the control unit 204 will supply no ignition current to a detonator 207. Consequently, an inflator 208 does not operate and an air bag 209 is prevented from becoming inflated as shown by reference numeral 210.
If the control unit 204 decides that the person on board is sitting on the seat 201 according to the signals from the weighing sensor 203 and the angle sensor 206, it determines the magnitude of collision according to an acceleration signal indicating an outbreak of such collision when the acceleration signal is supplied from a collision sensor 211. If the control unit 204 determines that the collision is serious, it supplies an ignition current to the detonator 207 to inflate the inflated condition 210 as shown by reference numeral 210 by activating the inflator 208 s0 as to protect the person on board. In FIG. 15, reference numeral 212 denotes a vehicle; and 213, an instrument panel. The detonator 207, the inflator 208, the air bag 209 and the like in the form of a unit are mounted in this instrument panel 213.
However, in the conventional apparatus for detecting the weight of a person sitting on a seat, because the weight sensor is provided only for the seat portion of the seat, the signal from the weighing sensor is corrected by an angle signal from the angle sensor that detects the reclining angle of the back portion of the seat. However, since a weight applied to the back portion 205 cannot be detected, there is a limit of correcting the signal from the weighing sensor, resulting in a problem that it is difficult to readily obtain a desired accuracy.
Referring to FIGS. 21-24, there is illustrated a conventional apparatus for detecting an auxiliary-seat mounting direction of the sort mentioned above.
A pair of antennas 303a, 303b which are wound like a coil on a flexible board are embedded in a bilaterally symmetrical position of the seating portion 302a of the seat portion 302 of a seat 301 such as an auxiliary seat, and the pair of antennas 303a, 303b are aued for simultaneously transmission and reception. Further, a pair of code generators 306, 307 (e.g., Transponder of Texas Instrument Co. (trade name)) are embedded in a position corresponding to the mounting position of the pair of antennas 303a, 303b in the seat portion 305a of an auxiliary seat 304 such as a child seat.
The pair of code generators 306, 307 are electromagnetically coupled to only the antenna 303a or 303b positioned right under the pair of code generators 306, 307. More specifically, as shown in FIG. 21, the antenna 303a is positioned right under the code generator 306 on one side and the antenna 303b is positioned right under the code generator 307 on the other when the auxiliary seat 304 is mounted on the seat 301 so that the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 face each other. Conversely, as shown in FIG. 24, the antenna 303b is positioned right under the code generator 306 on one side and the antenna 303a is positioned right under the code generator 307 on the other when the auxiliary seat 304 is mounted on the seat 301 so that the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 are directed in the same direction.
When the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 positionally face each other, the antenna 303a sends electric power to the code generator 306 on one side by means of an electromagnetic wave and raecives an ID code from the code generator 306, whereas the antenna 303b sends electric power to the code generator 307 on the other by means of an electromagnetic wave and receives an ID code from the code generator 307. When the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 are otherwise directed in the same direction positionally as shown in FIG. 24, the antenna 303a receives an ID code from the code generator 307 on one side, whereas the antenna 303b receives an ID code from the code generator 306 on the other.
Reference numeral 30B denotes an ID code reading circuit 308 for supplying electric power signals to the pair of antennas 303a, 303b periodically for a predetermined period of time after the power supply is put to work, receiving the ID codes received by the code generators 306, 307, reducing it into a signal which one of the antennas 303a, 303b receives which one of the ID codes so as to supply the resulting signals to a auxiliary-mounting-direction decision circuit 309. The auxiliary-mounting-direction decision circuit 309 determines the direction in which the auxiliary seat 304 is mounted on the seat 301 according to the input signal and sends either inflation permitting or prohibiting signal to an air-bag-inflation decision circuit 311
More specifically, when the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 positionally face each other an shown in FIG. 23, the auxiliary-mounting-direction decision circuit 309 receives a signal indicating that the antenna 303a is receiving the ID code from the code generator 306 and also receives a signal indicating that the antenna 303b is receiving the ID code from the code generator 307. Consequently, the auxiliary-mounting-direction decision circuit 309 sends the inflation prohibiting signal to the air-bag-inflation decision circuit 311.
When the back portion 302b of the seat 301 and the back portion 305b of the auxiliary seat 304 are otherwise directed in the same direction positionally as shown in FIG. 24, the auxiliary-mounting-direction decision circuit 309 receives a signal indicating that the antenna 303a is receiving the ID code from the code generator 307 and also receives a signal indicating that the antenna 303b is receiving the ID code from the code generator 306. Consequently, the auxiliary-mounting-direction decision circuit 309 sends the inflation permitting signal to the air-bag-inflation decision circuit 311.
When the air-bag-inflation decision circuit 311 determines an outbreak of serious collision according a signal from an acceleration sensor 310 while holding the inflation permitting signal from the auxiliary-mounting-direction decision circuit 309, the air-bag-inflation decision circuit 311 supplies an ignition current via an driving circuit 312 to an air-bag inflation detonator (not shown) incorporated in an air bag unit 313. Thus, an inflator is activated to inflate the air bag, whereby a child sitting on the auxiliary seat 304 is protected.
When the air-bag-inflation decision circuit 311 determines an outbreak of serious collision according the signal from the acceleration sensor 310 while holding the inflation prohibiting signal from the auxiliary-mounting-direction decision circuit 309, the air-bag-inflation decision circuit 311 supplies no ignition current to the air-bag inflation detonator. Thus, the air bag is not inflated and the auxiliary seat 304 is not pushed down from the rear side, so that the child is prevented from being knocked down onto the back portion 302b of the seat 301.
Incidentally, symbol A represents a vehicle; and B an instrument panel.
Notwithstanding, a pair of antennas have to be embedded in the seating portion of a seat in such an apparatus for detecting an auxiliary-seat mounting direction and therefore it is troublesome to mount the pair of antennas therein. Moreover, the external force applied each time a child is seated tends to develop trouble such as the disconnection of the antennas, thus necessitating repairs.
Subsequently, a schematic description will be given of a conventional person-on-board protecting apparatus as disclose in, for example, Japanese Patent Publication No. 519/1996 by reference to FIG. 27.
As shown in FIG. 27, an acceleration signal from an acceleration sensor 401 is converted via a pair of first and second incomplete series integration circuits 402, 403 to a displacement signal, which is supplied to an adder 404. A speed signal from the first incomplete integration circuit 402 is supplied via a second coefficient circuit 406 to the adder 404, and the acceleration signal from the acceleration sensor 401 is supplied via a first coefficient circuit 405 to the adder 404. Consequently, the adder 404 adds up the signals from the second incomplete integration circuit 403, the first coefficient circuit 405 and the second coefficient circuit 406 in order to obtain an estimated displacement quantity of the head of a person on board after the passage of a predetermined time after a collision. Further the adder 404 supplies an estimated displacement quantity to the following comparator 407 and outputs a trigger signal (an ignition signal) when the estimated displacement quantity exceeds a reference value of a control circuit 409. The comparator 407 has a reference value, which is varied by the control circuit 409 supplied with a position signal as switching transistors 410, 411, 412 connected in parallel are subjected to ON control (i.e., the output terminals A, Br C of the control circuit 409 shown in FIG. 4 of Japanese Patent Publication No. 519/1996 are at a high level, that is, "1"). Consequently, the comparator 407 outputs a signal so that the inflation timing of an air bag is hastened when a seat is pushed forward and delayed when the seat in pushed backward.
On the other hand, the acceleration signal from the acceleration sensor 401 is supplied to a collision decision circuit 413 where the-magnitude of the collision is determined. When the collision decision circuit 413 determines the collision to be serious, it outputs a high level signal to an AND gate 414. When the AND gate 414 is supplied with a signal indicating that judging from the comparator 407, the head of the person on board has reached the reference value at this time, further supplies a trigger signal to a detonator 416 via an inflation timing decision circuit, the collision decision circuit 413 and the driving circuit 415.
In this case, the first incomplete integration circuit 402, the second incomplete integration circuit 403, the adder 404, the first coefficient circuit 405 and the second coefficient circuit 406 constitute the inflation timing decision circuit (the section enclosed with a broken line of FIG. 27), which calculates the estimated displacement quantity of the head of the person on board due to a collision after the predetermined time. Further, the reference value of the comparator 407 is varied by the position signal from the seat position sensor 408 in accordance with the position of the person on board, so that when the air bag is sufficiently inflated, the head of the person on board precisely hits against the air bag. Reference characters 417a-417d in FIG. 27 form an ignition timing estimating means ranging from voltage dividing resistors over the inflation timing decision circuit, the resistors 417a-417d, the comparator 407 and the AND gate 414.
In such a conventional person-on-board protecting apparatus, since it has been arranged that the head of the person on board reaches a predetermined position after the passage of the predetermined time after the collision and hits against the air bag, the head position of the person on board varies with the angle of the back portion of the seat, for example, when the seat is reclined or not reclined, though the longitudinal position of the seat remains the same. In other words, the air bag that has completely been inflated-may not bump against the head of the person on board and when the seat is excessively drawn forward, the air bag that has completely been inflated may also not strike against the head thereof.
FIG. 30 shows a conventional apparatus for giving a warning about a seating condition by way of example.
As shown in FIG. 30, an infrared-beam emitting element 505 and a beam receiving element (not shown: incorporated in the infrared-beam emitting element 505) are provided in an instrument panel 504 disposed in front of a person on board 503 sitting on the seat 502 of a vehicle 501. The infrared-beam emitting element 505 is operated by a control-arithmetic circuit 507 to receive light reflected from the person on board 503 by means of the light receiving element, whereas the control-arithmetic circuit 507 calculates distances D1, D2 according to the trigonometrical measurement method. The control-arithmetic circuit 507 determines the presence or absence of the person on board 503 from the distances D1, D2 thus calculated and the sliding position L of the seat detected by an seating-position detecting sensor 508 and outputs a signal for allowing an air-bag device 509 for a passenger seat to operate when the person on board 503 sits on the seat. When the controlearithmetic circuit 507 determines that the person on board 503 is not sitting on the seat, it outputs a non-permit signal to the air-bag device 509 for a passenger seat and prohibits the air bag from inflating even when the air-bag device 509 for a passenger seat judges that a serious accident has occurred.
Since the air bag is inflated irrespective of the seating condition of the person on board 503 in the conventional apparatus for giving a warning about a seating condition, there has been the possibility that the air bag functions improperly even though it is inflated unless the person on board 3 is sitting on the seat in a right posture.
An apparatus for detecting the presence of a person on board which similar in type to the captioned apparatus has been described in, for example, Japanese Patent Publication No. 78539/1995 and the general description of such an apparatus will subsequently be given by reference to FIG. 39.
A steel plate forming the roof 602 of a vehicle 601 and a metal plate 604 embedded in the seating portion 603a of a seat 603 form a pair of electrode plates to form a capacitor C. When a person on board sits on a seat between the pair of electrode plates comprising the steel plate forming the roof 602, and the metal plate 604, the coefficient of electrostatic induction between the pair of electrode plates varies, so that whether the person is sitting on the seat 603 is detected by detecting a change in that coefficient.
Reference numeral 605 denotes an instrument panel provided in front of the driver's seat of the vehicle 601.
In such an apparatus for detecting the presence of a person on board, however, the space between the electrode plates is large because the electrostatic capacitance C is formed between the electrode plate installed beneath the seating portion of the seat and the steel plate formed on the ceiling of the vehicle. Thus, the electrostatic capacitance C formed therebetween is small and the problem is that a greater quantity of variation is impossible to secure even when the person enters between the electrode plates.